1. Field of the Invention
The present invention relates to a disc assembly for a magnetic disc apparatus. More particularly, it relates to a structure for mounting a temperature compensating disc in the magnetic disc apparatus.
2. Discussion of Background
Generally, a magnetic disc apparatus has a structure as shown in FIGS. 4 and 5. In the Figures, a symbol a designates generally a plurality of vertically arranged magnetic discs, a reference numeral 1(a.sub.o) designates a temperature compensating disc used as a dummy disc which is the same as the magnetic discs, a numeral 2 designates a clamp, a numeral 3 designates a plurality of spacers, a numeral 4 designates a rotating shaft, a numeral 5 designates fitting screws, a numeral 6 designates a plurality of magnetic heads opposing the surfaces of the magnetic discs a, a numeral 7 designates ginbal supporters for supporting the magnetic heads 6, a numeral 9 designates an actuator which moves the magnetic heads onto predetermined tracks in the magnetic discs, a numeral 10 designates a base, a numeral 11 designates a cover and a numeral 12 designates a spindle motor as a ootating source.
The temperature compensating disc 1(a0) and the plural magnetic discs a are mounted on the rotating shaft 4 at an equivalent distance by means of the spacers 3. The temperature compensating disc 1(a0) is placed above the uppermost position of the magnetic discs a by means of the clamp 2 and the screws 5. A desired number of the magnetic heads 6 are provided depending on the number of the magnetic discs a1, a2, a3 . . . . One surface of each of the magnetic discs a is used as a servo surface for the magnetic discs having a high track density.
The operation of the conventional disc assembly will be described.
When the rotating source 12 reaches a predetermined constant speed, one of the magnetic heads 6 is brought to a predetermined track position of one of the magnetic discs by the actuator 9 on the basis of a servo track, whereby writing-in or reading-out of data is carried out.
In the magnetic disc apparatus of this kind, the actuator 9 as a heat radiating source and the rotating source 12 are attached to the base 10. Accordingly, the temperature of parts placed near the base 10 becomes high and the temperature of parts placed near the cover 11 becomes low. Since the cover 11 has good heat radiating properties, the temperature of the uppermost magnetic disc 1(a0) becomes lower than that of the second magnetic disc a.sub.1 when a plurarity of the magnetic discs are vertically arranged, with the consequence that difference in temperature distribution between the uppermost magnetic disc and the second magnetic disc takes place. Since the difference in temperature distribution occurs due to self-heat radiation, the temperature difference just after a power source is turned on is different from the temperature difference after a certain time is passed. As a result, difference in thermal expansion among the magnetic discs a, the ginbal supporters and the arm heads 8 for supporting the magnetic heads takes place to thereby cause an off-track phenomenon. Therefore, in the conventional disc assembly for the magnetic disc apparatus, the uppermost magnetic disc a.sub.0 could not be used for a magnetic disc on which data is recorded, but was used as the temperature compensating disc 1.
Thus, in the conventional magnetic disc apparatus having the temperature compensating disc 1 which is not usuable as a data recording medium, the temperature compensating disc 1 occupies a space for a single magnetic disc a as the data recording medium. This results in reduction of the capacity of memory, or a long rotating shaft 4 in order to increase the number of the magnetic discs a, whereby the outer dimension of the magnetic disc apparatus becomes large.